Biometric feature recognition technology is expanding in the field of identity recognition. Biometric feature recognition technology uses imaging of user's intrinsic biometric feature such as fingerprints, iris, vein etc., as the basis for identity confirmation. Compared with password, identity card and other traditional means of identification, biometric feature recognition technology has many advantages, such as the individual is unique, no memory is needed, hard to be stolen, the operation is easy, and the security level is high. Especially on mobile terminals such as smartphones, tablets and laptops, biometric feature recognition technology is used as a safe and convenient means for identity recognition; and there is a trend to replace the traditional means of identity confirmation with biometric feature recognition technology. During the process of mobile terminal biometric identification, a camera is typically used for imaging. For example, the smartphone operating system can use the front camera to image the user's biometric feature, such as iris and face, at boot time or when an application requires a payment operation, and then confirms the user's identity by image processing.
At present, a camera of a mobile terminal generally uses filters facilitating imaging with visible light. This is because of the presence of light of various wavelengths in the nature; the human eye can recognize light (i.e., visible light) in the wavelength range between 320 nm-760 nm, light with wavelength larger than 760 nm (such as infrared light) can not be identified by the human eye. These invisible lights will affect the CCD or CMOS sensor in the camera, produce color distortion. Therefore, in order to solve the problem of color distortion and enhance the imaging effect, a low-pass filter is generally attached in front of the photosensitive device, which filter prevents the entry of invisible light.
On the other hand, studies show that for biometric feature imaging, especially for imaging iris, face, 3D Face, vein, infrared light (especially the near-infrared light) can achieve a better effect. For example, the iris imaging effects are not same for different races and different individuals. The pigment in iris organization of the white race and the black race is relatively shallow, it is thus easy to obtain a clear image with visible light; while the pigment in iris organization of the yellow race is relatively deep, it may thus be difficult to collect sufficient optical information for imaging with visible light. Infrared light imaging with infrared illumination and an additional filter attached in front of a photosensitive device improves imaging quality to meet the quality requirements of iris recognition algorithms and software, in which the additional filter allows near-infrared light to pass therethrough. In addition, the 3D face recognition using near-infrared light imaging has a higher recognition accuracy than recognition using visible light imaging, since the reflective property of the face skin will be better under infrared light, then the image sensor is able to receive more feature details to distinguish details depth information required by the 3D face recognition. However, as described above, the low-pass filter in the camera of a mobile terminal will prevent invisible light (comprising infrared light) from entering the photosensitive device; for such a mobile terminal, even if a filter allowing passing through of near-infrared light is additionally attached, near-infrared light imaging can not be performed yet.
One solution is to remove the low-pass filter in the camera of the mobile terminal, and only use a double-bandpass filter allowing passing through of both visible and infrared light to perform the infrared light imaging. However, when a camera with such a filter photographs, infrared light in the nature can also be allowed to pass therethrough, which causes the image captured in the sun to be obviously reddish; generally, it is very difficult to adjust the chromatic aberration with software, the imaging effect of photographing is affected.